闽西北建瓯马面山俯冲增生杂岩带内斜长角闪岩的地球化学、年代学特征及其地质意义

Geochemistry and Geochronology Characteristics of Diagonal Amphibole, within the Mamianshan Subbduction-accretionary Complex Zone,and its Geological Significance in Jianou City, Northwest Fujian Province

闽西北建瓯马面山俯冲增生杂岩由岩块和基质组成,其中变基性岩岩块有2类不同构造产状的斜长角闪岩:第一类与透辉石岩或大理岩呈似互层状产出;第二类单独呈构造岩块、团块状产于基质中,原岩均为玄武岩类,为幔源岩浆部分熔融的产物。通过元素地球化学特征分析,前者斜长角闪岩原岩为形成于类似洋岛-海山环境的碱性玄武岩;后者斜长角闪岩的原岩分别为岛弧钙碱性玄武岩和洋壳内部初始俯冲背景下前弧环境的MORB-like(类洋中脊)型岛弧拉斑玄武岩。通过锆石测年,前者斜长角闪岩的2组变质年龄为(399±3.5)Ma(MSWD=0.45)、(388±1.8)Ma(MSWD=1.19);后者斜长角闪岩的原岩结晶年龄为(441.8±4.7)Ma(MSWD=0.32),变质年龄为(411±19)Ma(MSWD=0.095)。通过对马面山俯冲增生杂岩带内发育的在空间上共生的斜长角闪岩类研究,其原岩形成于洋岛、前弧和岛弧等环境,结合锆石年龄和前人研究成果,认为华夏地块内部闽西北、浙西南一带发育早古生代末-晚古生代初的洋壳俯冲-弧陆碰撞(增生)造山作用。

There are two types of amphibolites within the Mamianshan subbduction-accretionary complex zone at Jianou city,northwest Fujian Province.The first is layer-liked amphibolites involved with diopsidites or marbles,the whole appeared tectonic blocks;another is the tectonic blocks of amphibolites alonely in the matrix.Geochemistry shows that the protolithes of two types of amphibolites are alkaline basaltic and basaltic,the magma formation were mainly controlled by partial melting process;the first type amphibolite was similar to OIB,the protolith may have originated from mantle magma within features like oceanic island or seamount basalts;another amphibolites have characteristics that be similar to CAB and Morb-like,the protolith formation may be at continental arc and fore-arc basin,occur in the initial stage of slab subduction within oceanic crust.Results of LA-ICP-MS zircon U-Pb dating show,the first type amphibolite have two groups metamorphic age(399±3.5)Ma(MSWD=0.45)and(388±1.80 Ma)(MSWD=1.19);another shows the rock-forming age was 441.8±4.7 Ma(MSWD=0.32)of the protolith,metamorphic age was(411±19)Ma(MSWD=0.095),and witnin metamorphic process between 402.8-393.5 Ma.Two types of amphibolites have different protolith、formation and tectonic setting,both appeared with tectonic blocks in the matri,offered the direct evidences for comfirmed the Mamianshan subbduction-accretionary complex.